JP4678600B2 - Pipe drawing plug and method of manufacturing pipe using the same - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a pipe drawing plug and a method for manufacturing a pipe using the same, and more particularly to a plug that is less likely to be worn and can have a long life and a method for manufacturing a pipe using the plug.

  Conventionally, when manufacturing pipes for various applications, pipes are drawn for the purpose of improving dimensional accuracy such as outer diameter, inner diameter, and wall thickness, improving surface smoothness, and ensuring mechanical strength. There is a case.

  For example, as shown in FIG. 1, the pipe is drawn by inserting a plug 1 ′ having a rear end supported by a mandrel M into the inner surface of the pipe P and drawing the pipe P in the direction of the arrow in FIG. . The plug 1 ′ is inserted into the inner surface of the pipe P so as to be concentric with the die 2 and the pipe P. At this time, the pipe P is deformed along the conical surface tapered portion 22 of the die 2 and the conical surface tapered portion 12 ′ of the plug 1 ′, while the cylindrical surface straight portion 21 and the plug of the die 2 are deformed. The diameter of the opening of the die 2 that is guided between the straight portions 11 ′ of the cylindrical surface 1 ′ and defined by the opposing straight portions 21 is the outer diameter, and the diameter of the straight portion 11 ′ of the plug 1 ′ Is processed into a pipe P having an inner diameter of.

  Here, in the conventional general plug 1 ′, the tapered portion 12 ′ and the straight portion 11 ′ are directly connected. In other words, as shown in FIG. 1B, the connecting portion between the tapered portion 12 ′ inclined with respect to the axial direction of the plug 1 ′ and the straight portion 11 ′ parallel to the axial direction of the plug 1 ′ is a point. It is a polygonal line that bends at S.

  When the inventors of the present invention have studied, in order to reduce the basic unit of the plug, if the conventional plug 1 ′ is repeatedly used for the drawing process of the pipe P without applying a surface coating, the tapered portion 12 ′ and It has been found that wear tends to occur in the vicinity of the connection part of the broken line with the straight part 11 ′. If the worn plug 1 ′ is used for the drawing process of the pipe P without taking care, the dimensional (inner diameter) accuracy of the pipe P after the drawing process may be deteriorated, or seizure may occur between the pipe P and the plug 1 ′. There is a problem that occurs. If only the plug 1 'is used for a long time, the worn plug 1' may be cut and polished and reused for drawing a pipe P having a smaller size. However, since the above reuse requires time for cutting and polishing, there is a problem that the production efficiency of the pipe P is lowered. Therefore, it is desired to develop a plug that does not easily wear and can be used for a long period of time for drawing a pipe P having the same dimension (long life).

On the other hand, plugs described in Patent Documents 1 and 2 have been proposed as plugs in which the tapered portion and the straight portion are not directly connected. More specifically, in the plug described in Patent Document 1, the tapered portion (the approach portion in Patent Document 1) and the straight portion (the bearing portion in Patent Document 1) are connected via the constricted portion (V-shaped groove). (See FIG. 2 in Patent Document 1). In the plug described in Patent Document 2, a tapered portion and a straight portion (finished portion in Patent Document 2) are connected via a recess as shown in FIG.
Japanese Patent Laid-Open No. 9-225522 JP 2003-112218 A

  However, the plug described in Patent Document 1 is intended to maintain a balance between the force in the pulling direction acting on the plug and the force acting in the opposite direction to the pulling direction (paragraph 0004 of Patent Document 1). There is only a constricted portion provided between the tapered portion and the straight portion, and there is no disclosure or suggestion about how the constricted portion affects the above-described wear of the plug. In addition, the plug described in Patent Document 2 is for the purpose of removing the bite and the like generated during the internal cutting, and making the inner peripheral surface of the pipe after the drawing process highly smooth (paragraph 0006 of Patent Document 2). In addition, only a recess is provided in a predetermined positional relationship between the taper portion and the straight portion, and there is no disclosure or suggestion about how the recess affects the above-described wear of the plug.

  The present invention has been made to solve the above-described problems of the prior art, and provides a plug that is less likely to be worn and that can maintain a long life and a method of manufacturing a pipe using the plug. Is an issue.

In order to solve the above-mentioned problems, the present invention provides a tube having a cylindrical straight portion inserted into an inner surface of a drawn tube and a conical tapered portion connected to the straight portion. In the drawing plug, the straight portion and the taper portion are connected to each other via a curved surface portion. In the sectional view in the axial direction, the curved portion has a curvature center at the straight portion and the taper portion. And having a radius of curvature of 2 mm or more and 20 mm or less located outside, the inclination of the vicinity of the connection point with the straight portion is substantially the same as the inclination of the straight portion, and the vicinity of the connection point with the taper portion An inclination of the tube is substantially the same as the inclination of the tapered portion, and a plug for drawing a tube is provided.

  In the pipe drawing plug according to the present invention, the straight portion and the tapered portion are not directly connected as in the prior art, but are connected continuously via a curved surface portion having a predetermined radius of curvature. In addition, the inclination of the curved portion near the connection point with the straight portion is substantially the same as the inclination of the straight portion, and the inclination of the curved portion near the connection point with the tapered portion is substantially the same as the inclination of the tapered portion. It is said that. In other words, the connecting portion between the straight portion and the curved surface portion and the connecting portion between the tapered portion and the curved surface portion do not form a broken line, and the straight portion, the curved surface portion, and the tapered portion are smoothly connected. Accordingly, the non-contact area that does not come into contact with the pipe during the drawing process of the pipe is smaller than that of the conventional plug, and the surface pressure acting from the pipe is dispersed (the maximum surface pressure acting near the non-contact area as described later). Will be reduced). Thereby, the wear of the plug in the vicinity of the non-contact region is unlikely to occur, and as a result, the lifetime can be kept long.

  Here, if the curvature radius of the curved surface portion is made too small, it approaches a conventional plug in which the straight portion and the taper portion are directly connected (the conventional plug corresponds to the curvature radius of the curved surface portion being zero). The effect of the above-described surface pressure dispersion becomes poor. On the other hand, if the curvature radius of the curved surface portion is too large, it is difficult to fix the plug at a specific position (axial position), and there is a possibility that the dimension (inner diameter) accuracy of the pipe after drawing is deteriorated. is there.

From the point of above, the radius of curvature is a 2mm or 20mm less.

  The present invention is also provided as a method for manufacturing a pipe, characterized by including a drawing process using the drawing plug.

  ADVANTAGE OF THE INVENTION According to this invention, it is possible to obtain the pipe | tube drawing process plug which is hard to produce wear and can maintain a long lifetime.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings as appropriate.
FIG. 2 is an axial sectional view showing a schematic configuration of a pipe drawing plug according to an embodiment of the present invention. FIG. 2A shows a pipe drawing process using the drawing plug. FIG. 2B is an enlarged view of a portion surrounded by a broken line in FIG. 2A.

  As shown in FIG. 2, the plug 1 according to the present embodiment is inserted into the inner surface of a pipe P that is drawn while being squeezed by a die 2, as in the prior art, and includes a straight portion 11 having a cylindrical surface shape, and a straight portion. 11 and a tapered portion 12 having a conical surface connected to 11.

  On the other hand, the plug 1 according to the present embodiment is different from the conventional one in that the straight portion 11 and the tapered portion 12 are connected via the curved surface portion 13. As shown in FIG. 2B, the curved surface portion 13 has a predetermined radius of curvature R in which the center of curvature is located outside the straight portion 11 and the taper portion 12 in the axial sectional view. The inclination of the curved surface portion 13 near the connection point 131 with the straight portion 11 is substantially the same as the inclination of the straight portion 12 (parallel to the axial direction of the plug 1). That is, the connection part of the straight part 11 and the curved surface part 13 is smoothly connected without forming a broken line shape. Similarly, the slope of the curved surface portion 13 near the connection point 132 with the tapered portion 12 is substantially the same as the slope of the tapered portion 12. That is, the connection part of the taper part 12 and the curved surface part 13 is smoothly connected without becoming a broken line shape. Thus, the straight part 11, the curved surface part 13, and the taper part 12 are smoothly connected to the plug 1 according to the present embodiment.

  Since the plug 1 according to the present embodiment has the above-described configuration, the non-contact area that does not come into contact with the pipe P when the pipe P is drawn is smaller than that of the conventional plug. As a result, the surface pressure acting from the pipe P is dispersed (the maximum surface pressure acting in the vicinity of the non-contact region is reduced). Hereinafter, this point will be described more specifically.

  FIG. 3 shows a pipe P obtained by drawing a pipe P having the same specification using each of the plug 1 having a curvature radius R = 10 mm and a plug having a curvature radius R = 0 mm (corresponding to a conventional plug) of the curved surface portion 13. It is a graph which shows an example of the result of having calculated the surface pressure which acts from numerical analysis. The horizontal axis in FIG. 3 indicates the axial position (mm) based on the point S (see FIG. 2) where the extension line of the straight part 11 and the extension line of the taper part 11 intersect (refer to FIG. 2). The surface pressure (MPa) calculated by numerical analysis is shown. In the numerical analysis, a finite element method (two-dimensional axis target elastic-plastic deformation FEM) was used.

  As shown in FIG. 3, in the conventional plug (R = 0 mm), the surface pressure increases rapidly in the vicinity of the reference point S, that is, in the vicinity of the broken line connecting portion between the tapered portion and the straight portion. This is considered to be caused by the occurrence of a non-contact region that does not contact the pipe P because the connection location is a polygonal line. In other words, since the surface pressure from the pipe P cannot act in the non-contact region, it is conceivable that the surface pressure acting on the region adjacent to the non-contact region suddenly increases.

  On the other hand, as shown in FIG. 3, in the plug 1 according to the present embodiment (R = 10 mm in the example shown in FIG. 3), the maximum surface pressure near the reference point S decreases. This is because the straight portion 11, the curved surface portion 13 and the tapered portion 12 are smoothly connected, so that the non-contact area that does not come into contact with the pipe P when the pipe P is drawn is less than the conventional plug. Conceivable. That is, since the non-contact area is small, it is considered that the surface pressure acting on the area adjacent to the non-contact area decreases as a result of the surface pressure acting on the pipe P being dispersed in the contact area.

  As can be seen from the results of the numerical analysis described above, the plug 1 according to the present embodiment has the straight portion 11, the curved surface portion 13, and the tapered portion 12 smoothly connected. The non-contact area that does not contact the pipe P is smaller than that of the conventional plug, and the surface pressure acting from the pipe P is dispersed (the maximum surface pressure acting near the non-contact area is reduced). Thereby, the wear of the plug 1 in the vicinity of the non-contact region is unlikely to occur, and as a result, the lifetime can be kept long.

  However, if the curvature radius R of the curved surface portion 13 is made too small, it approaches a conventional plug in which the straight portion 11 and the tapered portion 12 are directly connected (the conventional plug has a curvature radius R = 0 mm of the curved surface portion 13). Therefore, the effect of the surface pressure dispersion described above becomes poor. Therefore, the radius of curvature R is preferably 2 mm or more.

  On the other hand, if the curvature radius R of the curved surface portion 13 is excessively large, it is difficult to fix the plug 1 at a specific position (axial position), and the accuracy of the dimension (inner diameter) of the pipe P after drawing is deteriorated. There is a risk of inviting. Therefore, the radius of curvature R is preferably 20 mm or less.

  Hereinafter, the results of actually evaluating the life of the plug 1 according to this embodiment and the conventional plug will be described.

  Using a plurality of plugs having different curvature radii R, a test was conducted in which a tube having an outer diameter of 38.1 mm and a wall thickness of 3.8 mm was drawn and processed into a tube having an outer diameter of 22.55 mm and a wall thickness of 2.65 mm. And the life was evaluated by the total drawing length of the pipe until the dimension of the pipe after the drawing process was out of tolerance or seizure occurred between the pipe and the plug.

Table 1 shows the results of the above test.

  As shown in Table 1, the plug 1 (R = 2, 5, 10, 20, 30 mm) according to the present embodiment was able to maintain a longer life compared to the conventional plug (R = 0 mm). . In particular, if a plug having a radius of curvature R = 2 to 20 mm is used, it is possible to extend the life significantly compared to a conventional plug.

FIG. 1 is an axial sectional view showing a schematic configuration of a conventional pipe drawing plug, and FIG. 1A is an overall view showing a state in which the pipe is drawn using the drawing plug. FIG. 1B is an enlarged view of a portion surrounded by a broken line in FIG. FIG. 2 is an axial sectional view showing a schematic configuration of a pipe drawing plug according to an embodiment of the present invention. FIG. 2A shows a pipe drawing process using the drawing plug. FIG. 2B is an enlarged view of a portion surrounded by a broken line in FIG. 2A. FIG. 3 is a graph showing an example of the result of calculating the surface pressure acting on the plug from the pipe by numerical analysis.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Plug 2 ... Dies 11 ... Straight part of plug 12 ... Tapered part of plug 13 ... Curved surface part 21 ... Straight part of die 22 ... Taper part 131 of die | dye ..Connection point 132 with the straight portion of the curved surface portion of the plug ... Connection point with the taper portion of the curved surface portion of the plug M ... Mandrel P ... Tube

Claims (2)

A pipe plug for drawing a pipe, which is inserted into the inner surface of a pipe to be drawn and has a cylindrical straight portion and a conical tapered portion connected to the straight portion,
The straight portion and the tapered portion are connected via a curved surface portion,
In the axial cross-sectional view, the curved surface portion has a curvature radius of 2 mm or more and 20 mm or less located at the center of curvature outside the straight portion and the taper portion, and the inclination near the connection point with the straight portion is A pipe drawing plug characterized by being substantially the same as the inclination of the straight portion and having an inclination in the vicinity of a connection point with the tapered portion being substantially the same as the inclination of the tapered portion. A method of manufacturing a pipe, comprising a step of drawing using the drawing plug according to claim 1 .